Magnetocardiography (MCG) has been shown to offer powerful disease detection and diagnostic capabilities in both humans and animals not readily achieved with standard ECG and echocardiography, including the ability to map ischemic regions in the heart, and monitor arrhythmia. Fetal magnetocardiography (fMCG) has been successfully employed for the non-invasive study of arrhythmia and other conditions of the fetus in utero. However, due to the exceedingly small magnetic fields associated with the heart, current MCG systems use super conducting quantum interference devices (SQUID) as sensors. Complexities in fabricating and using SQUIDs, including coils, shielding, cooling and electronics, make them exceedingly expensive. These limitations have prevented MCG from achieving widespread clinical use. RMD proposes a new, solid-state, high density, 2-D sensor array that will revolutionize MCG technology so that it can be used in both the clinical setting with human subjects, and for research with animals to develop new treatments and pharmaceuticals. The proposed technology will make possible large area, high density, 2-D sensor arrays for excellent image resolution (~250 microns), high speed imaging without scanning, and sensitivity of ~10-13T/VHz. The sensors will also result in substantial reductions in both the complexity and cost of MCG instrumentation. The goal of the Phase I program is to show that the proposed technology can be used to perform MCG, and that the data can be mapped to produce images of the heart. RMD has assembled a strong research team consisting of a cardiologist, biophysicist, scientists and engineers to conduct the Phase I program. The team has substantial experience in measuring minute magnetic fields, and analyzing ECG in both animals and human subjects.